Progress Report P&F 6 - Identification of Immune Targets in Psoriatic Arthritis PI: Mark Soloski, Ph.D. We propose a series of studies aimed at identifying candidate molecular species targeted for immune recognition in Psoriatic Arthritis. In this study, we propose to: 1. Screen serum from Psoriatic Arthritis (PsA) patients and normal controls for the presence of antibodies reactive toward cellular protein species. 2. Identify and characterize the molecular species targeted for recognition by autoantiboclies in PsA using a proteomics based approach. In the initial phases of this study we have collected and archived serum, PMBCs and affected and unaffected skin samples from 43 normal and 23 PsA patients. In addition we have established a western blotting approach that we will employ to help identify proteins species targeted for recognition by PsA autoimmune serum. To date we have successfully tested keratinocyte cellular extracts with this western blotting approach for the presence of autoantigens targeted in SLE (U160k and PARP) and found the approach sensitive and reliable. We are currently generating cell extracts for a range of cell types which will be utilized in this approach.